1. Field of the Invention
This invention relates to a switched full-duplex Ethernet type communication network, particularly in avionics.
2. Description of the Related Art
The Ethernet network, which is the reference in the world of communication networks, can be used to send data in digital form by packets or “frames”, where a packet is defined as being a set of data sent in a single step on the network.
In an Ethernet network, the data in each packet are not interpreted. The network carries the data without understanding their meaning. A packet is composed of two types of data, network data that are used to route the packet to its correct destination, and useful data which comprise the “useful load” in the packet.
An Ethernet network is composed of different equipment that is subscribed to the network, and connected to each other through a communication means formed of active equipment called switches, which perform three functions:                connect network subscribers in point to point mode through physical links, which are physical supports for messages to be transferred, for example twisted pair cables,        route (switch) packets sent by source equipment to one or more destination equipment,        check the integrity and the format of the Ethernet packet.        
FIG. 1 illustrates an Ethernet network composed of two switches 11 interconnected to each other and each connected to three items of subscriber equipment 12 in point to point mode.
Operation of such a network is simple. Each network subscriber can send packets in digital form at any time towards one or several other subscribers. When a switch receives the packets, the “network information” data are analyzed to determine the destination equipment. The packets are then switched towards this equipment.
In the “switched full-duplex Ethernet type network” expression:                the “full-duplex” term means that the subscriber can send and receive packets at the same time on the same link,        the “switched” term means that the packets are switched in switches on appropriate outputs.        
For example, this network may be a 100 Mbits/s switched full-duplex type network on twisted pair; the term “twisted pair” means that connections between the equipment and the switches are composed of two pairs of cables, each pair being twisted; the term 100 Mbits/s simply means the transmission or reception speed of packets on the network.
The Ethernet technology imposes:                a minimum size and a maximum size on the packets,        an identification of the source and/or the destination(s) in each packet,        a CRC (“Cyclic Redundancy Check”) that checks the integrity of the transported data.        
At the present time, in the civil aeronautics field, data exchanges between the various onboard computers are based on the use of the ARINC 429 aeronautical standard.
However, the switched full-duplex Ethernet network is frequently used in industry. The emergence of new communication technologies shows that this type of network is an open and standard solution (IEEE standard 802.3) with a considerable potential for development as a local network. But this type of solution does not provide any means of guaranteeing segregation and transfer performances (in terms of network access, latency, etc.) necessary for avionics applications.